According to the tree I mentioned in your Sylvia thread, Ada Jane Clemesha, wife of William Wesley Clemesha Lecturer in Medicine, died in Surrey UK 18 Jun 1948. The actual cert is shown in the tree, as their original marriage cert. So it would appear that William would not have been free to marry Margarethe. The tree owner also indicates that William married Frances after the death of Ada.
This tree is a wealth of info if you can gain access to it through a personal sub or via public access through your library. One must be careful with trees, however, b/c they are only as accurate as the research carried out by the tree owner. In general, trees should be used as a guide to your own research. Having said that, this particular tree appears to have been well sourced with numerous attached records.
PB